Die-bonding is an important process in the packaging of integrated circuit packages. In the die-bonding process, dice that are cut from a wafer are taken out and bonded onto a substrate such as a lead frame for follow-up processes such as wire bonding and molding. Prior to bonding a die to a substrate, a paste-dispensing mechanism dispenses an adhesive agent onto the substrate. Then, a die pick-and-place mechanism of the die bonder places a die onto the substrate at the position where the adhesive agent has been dispensed. Finally, a heater is used to cure the adhesive agent so as to bond the die to the substrate.
In the electronics industry, various methods of dispensing adhesive agents have evolved to keep up with the rapid development of manufacturing needs for adhesives and conductive epoxies in a wide array of packaging assemblies. Dispensing applications have also expanded to other areas needed for new types of packaging encapsulation techniques. A wide variety of fluid materials with different viscosities are being used as adhesives, from solder paste, conductive adhesives and damming compound to fluxes, thermal paste and underfills. Various methods of dispensing are available such as stamping, stencil printing, jet-dispensing and nozzle or needle dispensing.
Stamping, which is also known as daubing or pin transfer, involves dipping a compliant tool into a reservoir of liquid adhesive and then transferring the liquid adhesive adhering to the tool onto a substrate such as a lead frame. This method is frequently used to attain very small dots or patterns of adhesive on the substrate, or when an adhesive is not suitable for dispensing through dispenser nozzles. A stamping system is illustrated in FIGS. 1 and 2 which show isometric and side views respectively of a conventional adhesive stamping system 100. The stamping system 100 comprises an adhesive disc 102 having a reservoir which holds an adhesive material 104, and a stamping pin 106 affixed to a stamping arm 108 which is designed to dip the stamping pin 106 into the adhesive material 104 and to transfer the adhesive material 104 on the stamping pin 106 onto a substrate placed at a stamping level.
Different types of adhesives may be required for bonding different dice onto a substrate. For instance, non-conductive adhesive may be used to bond blue and green light emitting diode (LED) dice while silver epoxy may be applied for bonding red LED dice. When a different adhesive is required, the adhesive disc 102 and the stamping pin 106 would have to be replaced accordingly to cater for the different adhesive. If the same stamping pin 106 and adhesive disc 102 are used for different adhesives, then the stamping pin 106 and the adhesive disc 102 have to be removed for cleaning before they used to transfer a different adhesive. This results in machine idle time and lengthens the operation process. Alternatively, to avoid having to remove or change any stamping pin and adhesive disc, each machine may be designated for handling one type of die or the same range of dice using the same type of adhesive. This results in increased costs due to duplication. Therefore, it would be desirable to provide a stamping system which allows the use of different adhesives while avoiding excessive machine idle time or duplicity.